Three dimensional radar transponder system

ABSTRACT

An independent system to evaluate three dimensional radars which derive their height information from slant range and beam elevation. This transponder system consists of two major units, one of which senses the ship attitude and transmits this information to the control station. The second major unit on shore receives this information and uses it to update and pre-set conditions of the transponder, in accordance with the ship attitude, to synthesize a target at a given range, elevation and azimuth when the radar uses a specific beam to determine the angle of elevation of the target above the horizon.

United States Patent 1191 Snaders THREE DIMENSIONAL RADAR TRANSPONDERSYSTEM [75] lnventor: Robert W. Sanders, San Diego,

Calif.

[73] Assignee: The United States of America as represented by theSecretary of the Navy, Washington, DC.

22 Filed: Sept.-2l, 1972 211 Appl. No: 291,120

1 1 Jan. 1,1974

3,263,228 7/1966 Abrahams et al 343/l7.7 3,295,l30 12/1966 Prestwood343/177 Primary Examiner-Malcolm F. Hubler Attorney-R. S. Sciascia etal.

[ 5 7 l ABSTRACT An independent system to evaluate three dimensionalradars which derive their height information from slant range and beamelevation. This transponder system consists of two major units, one ofwhich senses the ship attitude and transmits this information to the 52us. 01. 343/17.7 control Station The Second major unit on Shore [511Int. Cl. G015 7/40 ooivos this information and uses it to update and p[58] Field of Search 343/177 sot conditions of the transponder, iaccordance with the ship attitude, to synthesize a target at a given[56] References Cited range, elevation and azimuth when the radar uses aUMTED STATES PATENTS specific beam to determine the angle of elevationof 2,942,257 6/1960 Huntington 343/177 the FaFge-t above the homo3,308,461 3/1967 Von Fange 343/177 6 Claims, 5 Drawing Figures TRANSMITT 5 g ,3/ RADAR RECEIVE TRANSPONDER 28 i'}fi% DATA l DATA CONVERTERCONVERTER CONVERTER 7-22 26 TRANSMITTER z4az RECEIVER SHEET 1 0F 2TRANsIvIIT 30 SHIP 3D RECEIVE TRANSRCNDER RADAR i ?f}%g DATA DATACONVERTER CONVERTER CONVERTER 22 2a TRANSMITTER 24JZ RECEIVER PFEIEBJANH974 3, 783 .447

SHEET 2 OF 2 RECEIVE MIXER fog vIDEO RANGE DETECTOR AMPLIFIER DELAY 4 4-46 V 2 DIRECTIONAL COUPLER MIXER MODULATOR LOCAL FIXED W T OSCILLATOROSC/LLATOR i FROM DATA CONVERTER TRANsMIT 52 REFERENCE [6O 4 66 PHASVOLTA GE 5 FILTER CONTROLLED W COMPARATOR OSCILLATOR r6 8 DIvIDE BY "N HCOUNTER 1 FROM DATA CONVERTER THREE DIMENSIONAL'RADAR TRANSPONDER SYSTEMBACKGROUND OF THE INVENTION This invention relates in general to theaccuracy check of radars and more particularly to the accuracy check ofthree dimensional radars that derive their height information from Slantrange and beam elevation.

Two known means are currently used to check the accuracy of threedimensional radars one is by tracking a plane which is radar equipped,capable of tracking the ship and carries a precision altimeter. Slantrange and height information is exchanged between the plane and ship forcomparison. Azimuth information can be compared between the air searchradar ship aboard the ship, however, in most cases there will be someparalex introduced. The second known means is tracking targets ofopportunity in coordination with another ship in the same relative area.Correlation of the ships relative position with respect to the targetcan be utilized. In each of the known means used, errors will beintroduced by either system of the individual ship or plane that theother is not aware. Sufficient planes equipped and properly calibrated-for these types of missions would be relatively expensive both inequipment and man hours. Most three dimensional radars have built-inself-checks, but they are not independent of the systems.

SUMMARY OF THE INVENTION The present invention provides a means forevaluating three dimensional radars which derive their heightinformation from slant range and beam elevation. A radar target issynthesized at a predetermined range and elevation. Range is derivedfrom a pre-set counter which utilizes an accurately known time delay.The count is started by the received radar pulse from the ships radarand the delayed transponders reply is generated at the end of thepre-set count. Height is simulated by transmitting the delay pulse on apredetermined frequency that corresponds to that utilized by the shipsradar to generate the main lobe of the antenna pattern, the position ofwhich, with respect to the normal is frequency dependent. The shipboardportion of the system is utilized to sense both the ships attitude andantenna position, solve the trigimetric relationship and transmit thisinformation by data link to the control system on shore. The controlstation utilizes the received information to update the pre-setfrequency of the transponder to present a stable target even though theship may pitch or roll.

Accordingly, an object of the invention is to provide a system forchecking the accuracy of three dimensional radars.

Another object of the invention is to synthesize a radar target byradiating a signal using the proper frequency and precisely timed from aknown point with respect to the radar.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings.

BRIEF DESCIRPTION OF THE DRAWINGS FIG. 1 is a typical layout of the NAtesting situation;

FIG. 2 is a block diagram of a preferred embodiment of the invention;

FIG. 3 is a graphical representation of the various components used insolving the problem to derive the appropriate values;

FIG. 4 is a block diagram of the transponder used in the embodiment ofFIG. 2; and

FIG. 5 is a block diagram of the frequency synthesizer used in theembodiment of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The system embodying theinvention consists of two major subassemblies. The mobile stationcarrying the radar which is to be given the accuracy check and a fixedstation having a transponder which in response to a signal received fromthe mobile station will provide a three dimensional radar signal fortransmission to the mobile station. Since it is necessary to establishthe exact coordinates of the mobile station with respect to the controlstation other tracking stations may be utilized such as trackingstations 14 and 16.

The major sub-assembly aboard the ship 10 consists of the ships attitudeconverter 18, data converter 20 and data transmitter 22. Attitudeconverter 18 converts the ships attitude in pitch roll and ships antennaposition to digital form. A voltage representing the product of thecosine of the angle generated by the vector voltage representingposition of the ships antenna with respect to the ship and the vectorvoltage representing the ships attitude are combined and appear indigital form in data converter 20 and this signal is transmitted to thestation 12 via data link 24. For example, the ships attitude can berepresented in three dimension as shown in FIG. 3 with the Zaxis normalto the horizon, the X and Y axis representing magnitude of pitch androll with the X axis also representing the ships heading. Vector Arepresents the ships relative displacement from the normal to thehorizon and is shown by the angle. The vector B is the resultant vectorof the pitch and roll; the angle 0 is the angle with respect to theship's heading. Vector C is the vector representing the ships antennaposition as it rotates with respect to the ships own heading. Angle a isthe angle generated as the ships antenna rotates with respect to theships attitude vector. As the angle a develops the magnitude of vector Bwill vary with the ships attitude; therefore if by multiplying themagnitude of vector B by the cosine of angle a a voltage can bedeveloped which is directly related to the ships attitude at any giveninstant with respect to the antennas position. This information istransmitted to the station 10 via data link 24. It is necessary to knowthe magnitude and direction of the ships displacement with respect tothe horizon and the instant the ships three dimensional radar is lookingat the transponder. Utilizing the tracking stations 14 and 16 the shipstrue heading and position with respect to the transponder is known atthe instant of the mark signal. This information is then used tocorrelate with the transponders frequency and time delay to establishthe position of the synthesized target.

The second major sub-assembly is a receiver 26, data converter 28, andtransponder 30 located at the fixed station 12 which when evaluating athree dimensional radar position on a ship is positioned on theshoreline with the ship being positioned within radar range off thecoast. When the ships attitude information is received at receiver 26 itis converted by data converter 28 and fed to transponder 30. The signalreceived at transponder 30 from data converter 28 is used to modify thepreset frequency. Transponder 30 is preset to receive test signals fromthree dimensional radar 31 and reply on a specific frequencycorresponding to a given angle of elevation. Referring now to FIG. 4which shows the transponder 30 in more detail, the incoming signal fromthe three dimensional radar is fed to the first mixer 32 where it iscombined with the signal from the pre-tuned oscillator 34 which may bepre-tuned for a particular test. The resultant output signal is thepulse signal at the IF frequency which is fed to lF amplifier anddetector 36. The detected signal is further amplified in video amplifier38 to an amplitude sufficient to trigger range delay unit 40 whichshould be of the type that can be preset to any range within the rangecapability of the radar 31 (FIG. 2). Range delay 40 should be preset toa particular range for a given test. The output signal from range delayunit 40 is used to key modulator 42. Pre-tuned local oscillator 34 iscoupled through directional coupler 44 to first mixer 32 and to secondmixer 46. in the second mixer 46 the local oscillator signal from localoscillator 34 is combined with the RF signal from fixed oscillator 48which is tuned to the same frequency as the lF frequency. The outputsignal from the second mixer 46 is then the same frequency as theincoming signal from the three dimensional radar 35 but in CW form. Whenmodulator 42 is keyed by the output of range delay unit 40, a pulse isgenerated which is then amplified by TWT 50 and fed to antenna 52 andradiated back to the three dimensional radar 3S.

Pre-tuned local oscillator 34 is essentially a frequency synthesizer(FIG. which consist ofa very stable reference 60 such as a low frequencycrystal oscillator, a phase comparator 62, necessary filters 64, avoltage control oscillator 66 and a feedback loop 68 which consist of apresetable counter. The value of N in the feedback loop 68 will bedependent upon the value of the reference frequency 60 and the voltagecontrol oscillator frequencies as well as frequency increments necessaryfor generating the elevation scan loops, structure of the threedimensional radar. In addition to being preset by a given frequency itmust also have the capability of being updated as the ships attitudechanges.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. lt is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. In a three dimensional radar test system for testing threedimensional radars mounted on board a ship or other moving platforms thecombination comprising:

a. a three dimensional radar for transmitting test signals;

b. transmitter means located on the ship on which the three dimensionalradar is located for transmitting signals representing the shipsattitude and the position of the radar antenna with respect to the ship;

c. transponder means located on shore and having first antenna receivingmeans for receiving signals from said three dimensional radar and asecond antenna receiving means for receiving the signals transmitted bysaid transmitter means and transmitting a signal for reception by saidthree dimensional radar modified in accordance with the received signalsfrom said transmitting means to simulate a target for the radar beingtested.

2. The test system of claim 1 wherein said transmitter means includesconverter means for converting the ships pitch, roll, and antennaposition to digital form for transmission.

3. The system of claim 1 wherein said transponder comprises:

a. a first mixer having a first input for receiving signals transmittedfrom said three dimensional radar, a second input and an output; b. alocal oscillator being controlled by the signals received from saidtransmitting means, and having its output coupled to the second input ofsaid first mixer;

c. IF amplifier and detector circuit means coupled to the output of saidfirst mixer;

d. range delay circuit means coupled to and being responsive to thedetected signal out of said IF amplifier and detector circuit means forproducing an output delayed signal;

. a fixed frequency oscillator;

a second mixer having a first input coupled to the output of said localoscillator and a second input coupled to the output of said fixedfrequency oscillator and providing an output CW signal having the samefrequency as the frequency of the signal received at the first input ofsaid first mixer;

g. a modulator circuit means having a first input coupled to the outputof said second mixer and a second input coupled to the output of saidrange delay and being keyed by said range delay output signal;

h. a transmitter coupled to said modulator for transmitting a signalback to said three dimensional radar.

4. The system of claim 3 wherein said local oscillator is a frequencysynthesizer.

5. The system of claim 4 wherein said frequency synthesizer comprises:

a. a voltage controlled oscillator;

b. a reference oscillator;

c. a phase comparator having a first input coupled to said referenceoscillator, a second input and an output coupled to said voltagecontrolled oscillator;

d. a feedback loop coupled from the output of said voltage controlledoscillator to the second input of said phase comparator for providing acontrol voltage to said voltage controlled oscillator when there is aphase difference between the two inputs of said phase comparator.

6. The system of claim 4 wherein said feedback loop is a preset countercontrolled by the signals transmitted by said transmitting means.

rho

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3:7 3l7 Dated December 11, 1973 Inventor(s) Robert e Sanders It is certifiedthat error appears in the above-identified patent and that 'said LettersPatent are" hereby corrected as shown below:

On the cover sheet, in the second line under the heading,

change the spelling of the inventor's last name from "Snaders" toSanders Signed and sealed this ll th day of May 1971p (SEAL) Attest: v

EDWARD M.FLETCHER,JR o. MARSHALL DANN Attesting Officer CommissionerofPatents FORM PQ-IOSO (10-69) UNI ED STATES PATENT OFFICE CERTIFICATEOF CORRECTION Patent No. 3 3 Dated December" 3 Inventor) Robert w.Saneer-s It is certified that error appears in the above-identifiedpatent and thaosaid Letters Patent are" hereby corrected as shown below:

On the cover sheet, in the second line under the heading, change thespelling of the inventor's last name from "Snaders" to Sanders Signedand sealed this lL th day of May 19714..

(SEAL)- Attest:

T EDWARD M.FLETQHER,JR. j MAR HALL DANN Attesting Officer aCommissioner! of-Pate'nte (COMM-QC man-pea

1. In a three dimensional radar test system for testing threedimensional radars mounted on board a ship or other moving platforms thecombination comprising: a. a three dimensional radar for transmittingtest signals; b. transmitter means located on the ship on which thethree dimensional radar is located for transmitting signals representingthe ship''s attitude and the position of the radar antenna with respectto the ship; c. transponder means located on shore and having firstantenna receiving means for receiving signals from said threedimensional radar and a second antenna receiving means for receiving thesignals transmitted by said transmitter means and transmitting a signalfor reception by said three dimensional radar modified in accordancewith the received signals from said transmitting means to simulate atarget for the radar being tested.
 2. The test system of claim 1 whereinsaid transmitter means includes converter means for converting theship''s pitch, roll, and antenna position to digital form fortransmission.
 3. The system of claim 1 wherein said transpondercomprises: a. a first mixer having a first input for receiving signalstransmitted from said three dimensional radar, a second input and anoutput; b. a local oscillator being controlled by the signals receivedfrom said transmitting means, and having its output coupled to thesecond input of said first mixer; c. IF amplifier and detector circuitmeans coupled to the output of said first mixer; d. range delay circuitmeans coupled to and being responsive to the detected signal out of saidIF amplifier and detector circuit means for producing an output delayedsignal; e. a fixed frequency oscillator; f. a second mixer having afirst input coupled to the output of said local oscillator and a secondinput coupled to the output of said fixed frequency oscillator andproviding an output CW signal having the same frequency as the frequencyof the signal received at the first input of said first mixer; g. amodulator circuit means having a first input coupled to the output ofsaid second mixer and a second input coupled to the output of said rangedelay and being keyed by said range delay output signal; h. atransmitter coupled to said modulator for transmitting a signal back tosaid three dimensional radar.
 4. The system of claim 3 wherein saidlocal oscillator is a frequency synthesizer.
 5. The system of claim 4wherein said frequency synthesizer comprises: a. a voltage controlledoscillator; b. a reference oscillator; c. a phase comparator having afirst input coupled to said reference oscillator, a second input and anoutput coupled to said voltage controlled oscillator; d. a feedback loopcoupled from the output of said voltage controlled oscillator to thesecond input of said phase comparator for providing a control voltage tosaid voltage controlled oscillator when there is a phase differencebetween the two inputs of said phase comparator.
 6. The system of claim4 wherein said feedback loop is a preset counter controlled by thesignals transmitted by said transmitting means.